There are a wide variety of packages which include (1) a container, (2) a dispensing system extending as a unitary part of, or as an attachment to, the container, and (3) a fluent substance product contained within the container. One type of such a package employs one or more dispensing valves for discharging one or more streams of product (which may be a gas, liquid, cream, powder, or particulate product). See, for example, U.S. Pat. No. 5,271,531, U.S. Pat. No. 6,112,951, U.S. Pat. No. 6,230,940 and U.S. Pat. No. 7,086,575. Such valves are flexible and resilient, and have one or more self-sealing slits. Such valves can be mounted at one end of a bottle or container which typically has resiliently flexible side walls that can be squeezed to pressurize the container interior. The valve is normally closed and can withstand the weight of the product when the container is completely inverted, so that the product will not leak out unless the container is squeezed. When the container is squeezed and the interior is subjected to a sufficient increased pressure so that there is a predetermined minimum pressure differential across the valve, the valve opens. Such a valve can be designed so that it can also be opened merely by subjecting the exterior side of the valve to a sufficiently reduced pressure (e.g., as by sucking on the valve).
Such a type of valve can also be designed to stay open, at least until the pressure differential across the valve drops below a predetermined value. Such a valve can be designed to snap closed if the pressure differential across the open valve drops below a predetermined amount. The valve can also be designed to open inwardly to vent air into the container when the pressure within the container is less than the ambient external pressure, and this accommodates the return of the resilient container wall from an inwardly squeezed condition to the normal, unstressed condition.
Some other types of resilient, flexible, dispensing structures may instead have a small aperture that is always open at least a small amount (see, for example, the U.S. Pat. No. 6,547,808, column 4, lines 34-51 which describe a normally open orifice 24 with reference to FIG. 3 of the U.S. Pat. No. 6,547,808).